Separation of c2, c3 and c4 alkenes from highly cracked distillates



May 15, 1956 R. H. JoHNsToN ET Al. 2,745,889

SEPARATION oF c2, c3 AND c4 ALxENEs FROM HIGHLY CRACKED DISTILLATES 2Sheets-Sheet 1 Filed June 22, 1955 May 15, 1955 R. H. JOHNSTON ET AL2,745,889

SEPARATION oF c2, c3 AND c4 ALKENES FROM HIGHLY CRCKED DISTILLATES FiledJune 22, 1953 2 Sheets-Sheet 2 WNNN jnvenors UO E n T 0 Illlll +L -m .mnl man Ew NNN lod HAMM mmm mfm @NNJ .Mw/Mu I\ :M w nwmvm @NN A m A www HE A A Al' 4.H\\|| |W. #Hui ma im @N Au .m UO ..1 a AI .T J www a @NN 2N8N 4 @A @om mmmmow HW (2,535 l. om QN am@ f f @NN mmmom .T @mw .T N f27m t: f ,5mm vo United States i Patent() SEPARATION F Cz, C3 AND C4ALKENES FROM HIGHLY CRACKED DISTILLTES Robert :H: Johnston, Chatham, N.J., and George E. Mitchell, Baton Rouge, La., assignors to Esso ResearchandEngineeringCompany, a corporation of Delaware- Application June-22,1953, Serial No. 363,050 7 Claims. (Cl. 260-677) Thisinventionrelates'to the processing of light hydrocarbons producedjbyhgh-temperature'and low pressure cracking. Such hydrocarbons includein large proportiony Cz .toCe olens and diolens which'have tendencies to-polymerize very reactive carbons, whiehlinclude Cz-Ca alkenes WithCerlnaphtha,

are then forwarded to the firstofthe dual oil absorption systems,preferably through steps which will be`given in more detail.

.From-therst oil absorption,- a`relatively;dryjgas C2 fractionrich-methylene is 'obtained but this gas fraction has `to be furtherVtreated in the secondoil absorption for f additional properfractionation.

A lean absorption oil adopted for the second absorption comesvfrom theprimary fractionation, and the fat oil from the-second absorptionisreturned to thefpn'mary fractionator for stripping and release of lowboiling dioletnLA monomers at'elevated temperatures Vwhichcausedepolymei-ization. This is an important-featurefof 'recovering` the:C2-C6V unsaturated hydrocarbons as monomers. 2

The .primary fractionator, suitably' operated-fatrlow pressures and:high temperatures, .performs the functions:` of recrackinga-'orvdepolymerizing diene polymers Iin thef fat gas oil..absorbent from thesecond=oilvabsorlziernand,` of supplyingthe Vlean oil tothe second-oilabsorben At' the same time,the primary fractionator-supplies afheavierrecycle fraction as quench-to the hot icrackedwproduct stream entering-`this. fractionatorgand separates? overhead the Vcrackedlighthydrocarbons. whichinclude the recovered Cz-Cs components, andseparates a tar bottomsf.

older method of 1 processing high-i temperature cracked products yrichinrunsaturatediandfaromatic hydroek carbons isshown'in the-U. S. Patent,2,348,659 .of-BUI..

SmithretV al. It will readily be-seen howthe present-in` vention:clearly vdeparts therefrom .-by using.=the dualoil` absorption-systemsconjointly Withithe primaryfractiona-y tor and in several other specificfeatures.

The attached drawingpshowsl a owpla-nsof'stepsused to-accomplish theinvention Figgl shows a ow-plan-off major-steps used. Fig.Zshows.a-preferred"modilication.- for obtaining the lightyhydrocarbonestreampassed-fromf the rprimary fractionator tothe firstabsorber..

In Fig. 1 of the drawing, an .initialtotal-naphthm heavynaphtha,.kerosene,. gas oil,tor. heavier petroleumfeed.is... supplied byline 1 to a cracking unitl forcrackingatelef..

vated temperatures of V1000 to 1400?. Ffbut preferably low Therprocessing vto separate these hydrocarbons into cuts of .different-.molecular Weights Vhas to 'be ldone .with minimum Vtemperatures andpressuresof.I about-1 to-"Satmospherest Steam inhighl proportions4ofabout 50 to;90.mole percent are'- supplied .f to .reduce t the:ihydrocarbon .partialpressure 1 during' 'the crackin g and primaryfractionation.

The present.v invention is .not concerned/with details ol'thecrackingoperation but withprocessingcthe.'highly\ unsaturated'andaromatichydrocarbons characteristically resulting from thehighftemperature processes.' The ma-f terials'may be 'cracked ini-vaporphase-or mixed phase, usually in a fraction of a minute or afewminutesbywhat is known. as steam-cracking, uidf cracking or other kinds ofcracking processes..

Outlet line 3 leads eiuent hot cracked .products'from... the crackingunit 2 to a .low part of the primary'fractions. ator 4. Generally -aheavy fractiontfrom the primary fractionator, partly cooled in heat`exchanger 5,: is' recycled as a quenchinto the hot-cracked .products tolower theixztemperature. to .about 5400?-650? F: in :the outlet linev 3.before'they enterl the primary 'fractionator 4.

Primary -fractionator 4 is equipped'with. plates'or .equivf alentfractionating means andy is 'controlled in temperatures to1dist1'llVoverheadnlight hydrocarbons boiling up: to orthrough about 400 13.-460F.' or 500? F., .to form an intermediate gasoil boilinginthe .range ofaboutV 4003: Fior-.460 F; to 650 F., a heavier 4gas oil cycle stockfor-recycling as'quench oil, `and leave a tar bottoms.4 These resultsare obtained .with about v10 to .30 plates, aftopyvapor temperature of.about 200 F. to 400 F., intermediate :platetemperaturesriof '400 F. to550'." F. andzabottoms temperature-of550? Fito 700 F. underlow-pressures' of abouti to l0 atmospheres.

Thelight -hydrocarbonsdistilled.overhead are passed. byline 7 'throughaecooler Sinto receiver 9:Y Some of the condensate :in "receiver-9isreiuxedL by line 10zfor controlling top temperatures in fractionator'4; Aqueous condensate settled in receiver 9 may be drained byline 11x`A portion of hydrocarbonliquid distillate boiling, up` to about 400 F.or 500 F. is forwarded by line. 12 I to tank 13. Hydrocarbons, ggaseousand vvapor-ized, at i temperatures Vupto about. F.' atabout` l.atmosphere are :Withdrawn from' receiver 9: by -line 14-into.acompressing ,and cooling `system,- whichV mayl have one .or more.compressors,: reciprocal orcentrifugal, e.. g. compressor 15 and cooler16. In this compressing and. cooling system, higher than.C4 componentsare condensed in so far as possible inashort periodny Condensate 'fromthe-.compressingand coolingcan. be mixed with distillatepassed-fromweceiver'9 Nia line-12 intank. 13.v The 'sepa-.-rationfofathelight-Cz-Cr-components -from higher componentswvith minimumheatingand .exposure'is greatly e aided by using such steps fofpartialecondeusation by' compressing .-andfcooling;

The.` uncondensed f C1. i to `C4.{ gaseous hydrocarbon streamis` passedonfromftank 13 .byline k17. It may,l be'caustic 'scrubbedandwashed-.to-r-remove sulfur -contaminants in unit 18. This gaseousstream; preferably freedfof sulfur contaminants; is passed .by line :19into a low part of absorber v20.for removal ofCg and yhigher vcomponents, so yas to'leavemainly C1. and C2. components (methane,ethane,and ethylene) unabsorbed.- Since thislE absorber.functionsvmainly -toseparate C2 components itWillbetermedfa'fde-ethanizen As complete separat-ion offCz components asis-.praeticalris,desired atthis point The .de-'ethanizer, or. Yiirstyoil. absorbergin general,- opf. erates..witha.-topoverhead.gasstreamuemperature of.

about 60 to 75 F. for an inlet stream of abouti 80: tof.-

12051 F. under a pressure of -225 .to 275vp. .s. i. vg." Low boilingabsorbent oilaofmainlyCsand higher components, whichtboilmainlyzv-intherangefofml00 F, to200.- F; or..

tos4l0^Frisf-suppllied by line Z110-fthe 'uppenpart of y ab.y fe

sorber-L'ZO :at a `ratef of -.about:0.7. A10.1.0 :molesfrperI mole-r.of.l total feed. The heat otabsorptionsmay be removed by suitable heatexchange coolers or similar means. It is important that the low boilingabsorbent oil be a fraction from the products of the cracking operation.Use of an extraneous absorbent oil would result in degradation of theC-lcomponents of the absorber feed.

Additional amounts of C1 to C4+ hydrocarbons can be stripped from thecondensates passed from tank 13 by line 22 to stripping zone 23. Thisstripping zone has an overhead line 24 to cooler 25 from which reflux isreturned to the top by line 26 and bottom withdrawal line 27 forCs-icomponents. The Cr to (24+ components in the overhead distillate arepassed by line 28 to the absorber 20.

- The temperatures in the lower stripping section of the de-ethanizerdepend on the volatility of the lean oil. By using the light lean oil,low temperatures, e. g. preferably below 300 F. can be used in thestripping section to minimize product degradation and equipment fouling.It is significant to note that the lean absorbent oil fed by line 21 tothe upper part of the de-ethanizer 20 does not have a criticalrequirement on the lowest boiling components, since any methane, ethaneand ethene components present will be taken overhead satisfactorily.

In any event the overhead CiCz (methane, ethane, and ethene) mixture ispassed by line 29 to the second absorber 30 to be treated therein with amore non-volatile oil absorbent, which absorbs a small amount of the C1to C2 hydrocarbons in absorbing practically all C3 and higher componentspresent. This second oil absorber makes a good clean up4 of componentshaving higher molecular weights than the C2 components to give anoverhead rainate of concentrated ethene containing less than about .01%of such higher molecular Weight components. Use of the second absorberalso makes it post sible to operate the rst absorber with thecombination of light C5| lean oil, relatively low temperatures andpressures, and bottoms product essentially free of C2 and lightercomponents.

A further advantage of using the second absorber in combination with theprimary fractionator is that the absorbed C3 and higher components arebrought back for recovery in the cyclic system.

The de-ethanizer overhead stream may contain more C5 to Cs componentsthan C3 to C4 components, and they will be fully removed in the secondabsorber, then -be recovered by stripping from the fat cycle oil in theprimary fractionator 4.

The second absorber 30 receives the CrCz-- stream from line 29 at about70 F. to 80 F. or about 72 F. at 245 p. s. i. g. The lean gas oil orlean cycle oil is passed into the upper part of the second absorber 30at about 60 F. from line 31 to flow countercurrently to the CrCz gaseoushydrocarbons, which are to be taken overhead at about 70 F. through line32.

The fat absorbent cycle oil is withdrawn from the bottom part of thesecond absorber 30 at about 72 F. by line 33, is preheated in heatexchanger 34, then flowed into the primary fractionator 4 at about 300F. to 400 F., or say 360 F.

The fat absorbent cycle oil returned from the second absorber 30 by line33 into primary fractionator 4, is subjected to temperatures best suitedfor depolymerizing dimers and polymers of C5+ dienes, such asdicyclopentadiene and the like. These temperatures are in the range of350 F. to 650 F. The resulting monomeric dienes are swept out quickly asthey are diluted by other hydrocarbons being distilled in fractionator4. The thus recovered diene monomers are reprocessed in the mannerexplained.

A side stream of the cycle oil, which is a light gas oil, is withdrawnby line 35 to a side stream stripper 36 for vapor pressure adjustment bypractically complete stripping of hydrocarbons boiling below about 460F. that are returned to primary fractionator 4 by line 37. Steam may beused to aid thestripping in stripper 36. The

stripped cycle oil is passed from the bottom of stripper 36 byline 38through heat exchanger 34, where this oil is lowered in temperature fromabove 420 F. to below 150 F. and then through cooler 39 for furthercooling. The stripped or lean cycle oil should be about 60 F. in theline 31 on being passed into the top of the 2nd absorber 30.

Returning attention to the de-ethanizer or first absorber 20, whereinthe gaseous hydrocarbons are scrubbed under conditions to leave mainlymethane, ethane, and ethene in the overhead gas, it is to be seen thatthe fat absorbent naphtha oil is withdrawn from the bottom by line 40for processing to segregate a propene C3 concentrate, and abutene-butadiene C4 concentrate. As in the earlier described steps, atthis point it is again desirable to use low temperatures and minimumresidence periods in the separation of the C4 and C5 dienes.

The fat oil from the de-ethanizer is led by line 40 into the desorptioncolumn 41, which will be termed a debutanizer since it serves toseparate C4 and lower components from the C54,- naphtha. Column 41provided with fractionating plates or equivalents preferably acts as aflash zone in having a lower pressure of about p. s. i. g. or lower forquick vaporization of C4 and lower components. The distillation of theC4 and C3 components from the C5+ absorbent oil is carried out atsuitably low temperatures. Bottoms of column 41 may be heated up toabout 350 F. for removing small amounts of C4 and C3 components, leavingCs-llean solvent to be withdrawn by line 42. A portion of theCs-lresidual fraction is diverted through cooler 43 into the line 21 tobe recycled to the de-ethanizer. The other portion of the stripped C5|fraction is used for recovering valuable components, such ascyclopentadiene, isoprene, piperylene, benzene, toluene, methylcyclopentadiene, and xylenes and other resin raw materials.

Overhead from column 41 is passed by line 44 to cooler 45 for total orpartial condensation. Some condensate is relluxed by line 46. Theremaining distillate from column 41 is passed by line 47 todepropanizingcolumn 48 to separate a propylene-rich C3 fraction overheadand a butene-butadiene-rich C4 bottoms. The C3 overhead is passed byline 49 to condenser 50. Reux is sent back by line 50 and remaining C3distillate product is removed by line 52. The C4 product is removed byline 53.

Columns 41 and 48 may be equipped with about 40 plates, usual reboilingmeans, etc.

In the modification of Fig. 2, the means serving the same functions asin Fig. 1 are given similar reference numerals. Thus, tank 209 in Fig. 2serves like tank 9 in Fig. 1 to collect partially condensed gaseoushydrocarbons and naphtha distillate via line 207 from a primaryfractionator. The gaseous hydrocarbons are removed by line 214 to becompressed by compressor 215thencommingled with liquid naphtha from line212.

The combined hydrocarbon streams are passed through cooler 216 into tank213, which corresponds to tank 13 in Fig. 1.

The uncondensed gaseous hydrocarbons are taken by line 217 from tank 213to be subjected to a second stage of compression and cooling before adesulfurization in l scrubber 218. The desulfurized C1 to C4hydrocarbons are passed from the vessel 218 by line 219 into thedeethanizer or first absorber 220 which corresponds to vessel 20 in Fig.1.

Condensate from tank 213 is passed by line 222 into fractionator 223 forquick separation of components that boil below 200 F. from higherboiling components.

Here short hold up time is important for reducing polymerization losses.Fractionator 223, like fractionator 23 in Fig. 1, is operated underpressures of about 10 p.'s. i. g., top temperatures of about F. to 190F., and bottoms temperatures of about 300 F. to 320 F.

The overhead of vfractionator 223 is taken by line 224 to condenser 225.Redux is' returned by line 226 to fractionator 223. Bottoms fromfractionator 223 maybe partly recycled through areboiler 254. The netamount of bottoms may bewithdrawn through line 227 to a preheater255forpreheating the feed for the fractionator 213.

'Ihe uncondensed. gaseous C1 to C4 hydrocarbons from tank Z13-arepassedV by line 217 to'second stage compressors 256. Afterthiscompression, these hydrocarbons, gaseous and partially condensed,may be mixed with liquid distillate taken by line 228 from fractionator223 for coolingr in` cooler 257V before being passed-by line 258 intodrum' 259 for/additional gasl separation.

The gaseous C1 tov CH- components are-passed by line 260 vto the causticsoda scrubber 218 for removal of sulfur contaminants. The .desulfurizedgaseous hydrocarbons are passed by line 219 into a low part of rstabsorber 229 which is fed with C5+ liquid naphtha solvent from line 221.

The condensate from separator 259 may be passed by line 261 tocausticsoda contactor 262 for removal of sulfur contaminants. The scrubbedcondensate is passed by line 263 into absorber'220 at about the sametray where gaseous hydrocarbons'are fed by line'219.

The overhead product removed by line. 229 from column-220'may lthen betreated in the same manner as the overhead from column J 20 described inconnection with Fig.v 1. The-bottom product removed by line 24) shouldbe treated in the same manner as bottoms taken by line 4 from column2tand described in connection with Fig, l.

The segregationof C3 and C4 components from the bottoms of therstabsorber is simplified. by having had the C2 andlighter componentsfully eliminated. The separations: of. thepCa, C4, and higher componentsbenefit from the lowered pressures which in turn make the fractionationtemperatures lower.

The sequence of first stripping the C3-C4 mixture from the fat oilof thefirst absorber in the de-butanizer 4i is of additionalimportance forminimizing equipment fouling. It has been found that the fractionatorbottoms tem peratureis best adjusted to a low level if theCs-lfat.absorbentoil'is stripped of the C3 together with C4 components ratherthan if it is first only of C3 components. The temperatures towhichtheCr and the C5+ components are exposed are lower, and the C5+ materialis subjected 6 the first absorber or de-ethanizer, these lighthydrocarbons including very reactive C44 dienes are segregated mostsuitably by the combination of partial condensation through compressionand cooling Vwith fractional. distillation in order to minimize lossesand fouling.

in the rst absorber 20y offFig. l, 220 of Fig. 2, it is important tohave as nearlycomplete removal of C2 and C1 components from the bottomsas possible. 'With the dual absorber system; the first absorber. can bemade to function in this directionl for increasing recovery of ethyleneand minimizing pressures and temperatures in following fractionationequipment.

The temperatures in 'the stripping sections of vthe irst absorber(de-ethanizer) and of the'debutanizer are largely dependent upon thevolatility of the C54- naphtha used as the lean solvent oil. This lightvolatile leanoil keeps temperatures at a minimum in these strippingsections. Thus product degradation and equipment fouling'are reduced.

The circulation of the leanoil is based on the number of moles of thelean oil required to obtain the-necessary absorption. Since there -arevmore molesy per barrel of light distillate than of heavier distillate,the `light lean oil can be used with considerably lower circulationrate.

By using the C5-1- light lean oil in the rst absorber, recovery ofcyclopentadiene and methyl cyclopentadiene can be'increased. Anycyclopentadiene and methyl cyclopentadiene dimerized during holdup'isnot lost to a high boiling fraction, but merely give ahigh'di'stillation tail which can be recovered as a residual dimerconcentrate.

The use of the light lean oil in the C5 to 200 F. range has the furtheradvantage combining the strippingand debutanization into a single step.

The use of the heavier` cycle or gas oil in the secondabsorber clean-upof the dry CrC2+ gas makes possible the use of the light lean oil in theiirst absorber where the desired defethanizing is carried out. Theheavier cycle oil used in the second absorber is not processed through.stripping sections of the light end towers. Recovery of monomeric dienesfrom the cycle oil is favorably made to takeplace in the. primaryfractionator.

For the purpose of illustration, the followingcompositions of majorstreams to .and from the dual absorbers are presented.

TABLE Principal components of major streams 1 Debutanzer feed, bottom ofcolumn 2O to column 4l,

2 Vapor feed to 2nd absorber which uses cycle gos oil as lean solvent.

3 Fat oil containing mainly ethylene (CF) and C5: diene monomers andpolymers forrecycle from bottom of 2nd absorber 30 to primaryfractionator 4 for contact with cracked stream.

to only a single distillation operation in this preferred sequence ofdebutanizing and depropanizing. In addition to reduced equipment foulingand degradation of products, molecular weight increases resulting frompolymerization of the circulating C5| lean oil are minimized.

Between the primary fractionator, where the light hydrocarbons areseparated from heavier cracked products, and

What is claimed is:

l. The process of separating a narrow ethene-rich fraction fromhigh-temperature cracked light hydrocarbon gaseous products strippedfrom higher-boiling products in a primary fractionator and separatedfrom overhead distillate thereof, which comprises passing a stream ofsaid gaseous products first through an absorption zone 7 Y where saidstream is contacted with a CsA-'hydrocarbon fraction to remove most ofthe C3 and higher components, said Cs-lhydrocarbon fraction being passedinto said absorption zone after being stripped free of C3 and C4components, then passing the remaining ethene-rich stream into contactwith a light gas oil from the primary fractionator to removesubstantially all remaining C diene and higher components by absorptionin said oil, and returning said gas oil containing absorbed C54-components to the primary fractionator.

2. The process of separating narrow C2, C3, and C4 fractions from hightemperature cracked products, which comprises separating the bulk of theC3 and C4 components by absorption in a lean Cs-lnaphtha containingmainly dienes and aromatics in a lirst absorption zone to leave methane,ethane, and ethene in a gaseous C1C2+ stream, passing said C54- naphthaenriched by the ab sorbed C3 and C4 components but substantially free ofC2 components into a fractionating zone wherein the C3 and C4 componentsare distilled o under lowered pressure, passing the gaseous C1Cz+ streaminto a second absorption system in which a cracked gas oil fractionabsorbs remaining amounts of C3 and higher molecular weight componentsfrom the gaseous CiCz-- stream to form a C2 rich fraction leftunabsorbed, and fractionating a narrow Cs fraction from the C4components with which they are distilled from the Cs-lnaphtha.

3. The process of separating C2, C3, and C4 fractions from a hightemperature cracked hydrocarbon product vapor stream containing mainlyalkenes, dienes, and aromatics, which comprises maintaining most of theC2 to C4 hydrocarbons in vapor phase While higher molecular weightcomponents are condensed therefrom by quenching, compressing andcooling, absorbing C3 and C4 components from the vapor stream incondensed C54- hydrocarbon liquids under pressure, under conditionsleaving Cz and lower components unabsorbed, and distilling absorbed C3and C4 components' from said C5+ liquids under a lowered pressure.

4. The process of separating C2, C3 and C4 fractions from ahigh-temperature cracked hydrocarbon product vapor stream, whichcomprises separating from said stream a light gas oil fraction boilingmainly in the range of 460 F. to 650 F. in a primary fractionating zone,separating from said Vapor stream passed overhead from saidfractionating zone a light naphtha fraction boiling mainly in the rangeof 100 F. to 200 F. to obtain a remaining vapor stream rich in C2, C3and C4 componv C4 components in said light naphtha, and treating theremaining vapor stream rich in ethene with a heavier lean oil to absorbtherefrom C3 and higher components in a second absorber. Y

5. The process of claim 4, in which the light gas oil fraction boilingmainly in the range of 460 F. to 650 F. is taken from said primaryfractionating zone to be used as said heavier lean oil.

6. The process of separating C2, C3 and C4 fractions from ahigh-temperature cracked hydrocarbon product vapor stream containingmainly alkenes, dienes, and aromarics, which comprises separating theC2, C3 and C4 components with C54- naphtha components as a distillateoverhead in a primary fractionation zone, concentrating the C2components in a gas-phase stream by compressing and cooling a gas-phaseseparated from said overhead distillate, eliminating sulfur contaminantsfrom the gasphase stream, contacting the gas-phase'stream with C54-naphtha hydrocarbon liquid to absorb therefrom Cs and C4 components butleaving substantially al1 C2 components unabsorbed, thereafter strippingthe absorbed C3 components together with C4 components from theCs-lnaphtha hydrocarbon liquid under lowered pressure.

7. The process of separating C2, Cs and C4 components from ahigh-temperature cracked hydrocarbon vapor stream rich in C1 to C4|alkenes and dienes, which comprises partially condensing C4+ componentsfrom said vapor stream by compressing and cooling said vapor stream,stripping by fractional distillation mainly C4 and lower molecularWeight components from the resulting partial condensate, remixinguncondensed components of said vapor stream with the C4 and lowermolecular Weight components stripped from the partial ycondensate toobtain a stream rich in C1 to C4 hydrocarbons, and passing said streamrich in Ci to C4 hydrocarbons into contact with a naphtha hydrocarbonfraction boiling mainly in the range of F. to 200 F. to absorb most ofthe C3 and C4 components but to leave the C2 and lower componentsunabsorbed from the resulting C2 rich gas.

References Cited in the le of this patent UNITED STATES PATENTS2,348,659 Smith et al May 9, 1944 2,377,736 White June 5, 1945 2,413,503Katz Dec. 31, 1946 2,514,294 Rupp July 4, 1950 t. /MM e

1. THE PROCESS OF SEPARATING A NARROW ETHENE-RICH FRACTION FROMHIGH-TEMPERATURE CRACKED LIGHT HYDROCARBON GASEOUS PRODUCTS STRIPPEDFROM HIGHER-BOILING PRODUCTS IN A PRIMARY FRACTIONATOR AND SEPARATEDFROM OVERHEAD DISTILLATE THEREOF, WHICH COMPRISES PASSING A STREAM OFSAID GASEOUS PRODUCTS FIRST THROUGH AN ABSORPTION ZONE WHERE SAID STREAMIS CONTACTED WITH A C5+ HYDROCARBON FRACTION TO REMOVE MOST OF THE C3AND HIGHER COMPONENTS, SAID C5+ HYDROCARBON FRACTION BEING PASSED INTOSAID ABSORPTION ZONE AFTER BEING STRIPPED FREE OF C3 AND C4 COMPONENTS,THEN PASSING THE REMAINING ETHENE-RICH STREAM INTO CONTACT WITH A LIGHTGAS OIL FROM THE PRIMARY FRACTIONATOR TO REMOVE SUBSTANTIALLY ALLREMAINING C5 DIENE AND HIGHER COMPONENTS BY ABSORPTION IN SAID OIL,